To guarantee the safety of an EMU train during its practical travelling, bogies (i.e. travel units) of the EMU train are required to be replaced and maintained at certain intervals. Thus, it is necessary to lift the whole train to a proper height to take off the bogies. For this purpose, a lifting jack is necessary.
An under-floor lifting jack consists of bogie lifting means with lifting rails arranged in several spaced pits and body hoists arranged at both sides of the bogie lifting means. Fixed rails arranged on the ground between adjacent pits and the lifting rails of the bogie lifting means form a continuous track on which the EMU train and the bogies may travel. The EMU train usually consists of a basic unit of 8 cars, and each of the cars has two bogies. The bogie lifting means can lift the whole train and the bogies together to a proper height. After the lifting, the body hoists lift and maintain the car bodies at the height, and then the bogies are disconnected from the car bodies and lowered along with the bogie lifting means, and separated from the car bodies.
The UFLJ is indispensable equipment for the repair and maintenance of the EMU train, and can be used to change all bogies of a whole EMU train without uncoupling the train or to repair and maintain any single bogie of a car after the train is uncoupled. The prevalent EMU train in China usually consists of a basic unit of 8 cars including two locomotives and 6 intermediate cars. In practice, two basic 8-cars units can be linked to form a 16-cars EMU train, which, however, is always uncoupled into two basic units for repair and maintenance. In China, the four types of EMU trains, i.e. CRH1, CRH2, CRH3 and CRH5, production of which began
TABLE 1Geometry ParameterLength (mm)FixedCarWheelIntermediateTreadDistanceWidthDiameterTypeTrainsetLocomotiveCar(mm)(mm)(mm)(mm)CRH121400026950266002700190003331915CRH220140025700250002500175003380860CRH320068525675247752500173753265920CRH521500027600275002700190003200890in 2007, have become the main high-speed railway passenger trains. Since such four types of EMU trains are different from each other in dimensions such as the total length, locomotive length, intermediate-car length, the tread (i.e. the distance between two wheels of a wheel-set), the fixed distance (i.e. a distance between centers of two bogies of a car) and the car width (as shown in Table 1 below). For any existing UFLJ in the world, both the distances between adjacent pits and lengths of the bogie lifting means are the same and correspond to the lengths of the respective type of train. As a result, each of the UFLJs only matches one type of EMU train. Therefore, the existing UFLJs all over the world are not compatible with all the four types of EMU trains.
Due to the tight-lock type coupler between cars of the EMU train, the permitted height tolerance between cars during the lifting process in repair & maintenance is strictly confined to ±4 mm, which requires the UFLJ to be equipped with an accurate positioning function and a synchronous lifting & lowering function. A concentrated repair and maintenance mode is adopted for the EMU trains in maintenance bases (e.g. an EMU depot) in China. Each of the maintenance bases is built for several or all types of EMU trains. If one type of UFLJ is designed for a single type of EMU train, a great waste would occur for the construction of the EMU train maintenance bases. Thus, the compatibility of the UFLJ is essential.